The present invention relates generally to interior wall construction products, and more specifically to apparatus used for finishing corners created by adjacent edges of wallboard sheets.
In conventional interior construction, wallboard or drywall panels are secured to a framework of vertically and horizontally arranged frame members, typically wood or metal. Abutting edges of adjacent wallboard panels are finished using a combination of wallboard joint tape and wallboard joint compound as is well known in the art. When adjacent wallboard panels are configured to form corners, corner bead products are often installed for both aesthetics and utility. Corner beads are more commonly used on outside corners, but there has been some development of corner beads for inside corners as well.
Corner beads finish a rough corner into a pleasing symmetrical transition with the respective adjoining walls, and also provide some resistance to abuse and impact on the corner. To accomplish these tasks, a suitable corner bead product should fit snugly on the wall, be easy to attach, and have material and design properties that allow it to resist at least minor impacts without severe damage or detachment from the wall.
Conventional corner bead strips are either made of metal or various types of plastic, and are provided in relatively rigid lengths or in flexible rolls. Flexible corner bead strips are typically two types. In the first type, 2 metal strips approximately 0.010-0.015 inch thick are disposed parallel to each other, are laminated to a web of paper with a slight separation gap between the strips so that the strip may be flexed as desired to match the corner profile. The flex bead strips are then applied to the wall corner and secured using wallboard joint compound. Disadvantages of conventional flexible metal corner bead strips include that the metal is relatively heavy, expensive, is easily bent or kinked, and is often difficult to straighten completely when provided in rolled form. In addition, due to the gap between the adjacent strips, it is sometimes difficult to obtain a straight or plumb corner edge, and also the actual corner of the wall is only protected by paper, and as such is prone to impact damage. Conventional flexible plastic corner bead strips suffer from the same susceptibility to impact damage at the wall corner.
Plastic corner bead strips can be made from a single strip of flexible plastic that is laminated to a paper web. Compared to the above-described metal strips, plastic corner strips are thicker, about 0.25 to 0.55 inch, to provide comparable rigidity to metal. However, the profile of the plastic strip is thinner near the centerline, to facilitate flexing for conforming to the corner profile.
One design criteria of flexible plastic corner bead strips is that a compromise is usually needed between a plastic that is sufficiently rigid for protecting the corner, which may include gaps between the wallboard edges, but sufficiently flexible for conforming to the wall without pulling away from the wall due to inherent bias of the strip to remain generally planar.